Linear piezoelectric motor employing internal feedback

Abstract

A piezoelectric motor system is formed with a piezoelectric motor incorporating an element that is physically displaced as a function of an applied voltage resulting in the generation of a back electromotive force. The system incorporates a controller having an output connected to the piezoelectric motor. The controller receives a direction signal indicating the desired drive direction of the piezoelectric motor and a velocity signal indicating the desired velocity of the piezoelectric motor. The controller provides a drive voltage for driving the piezoelectric motor in the desired drive direction. An electrical equivalent circuit that mirrors the electrical characteristics of the piezoelectric motor is connected to receive the drive voltage from the controller. A comparator provides a difference signal indicative of the difference in voltage developed across the piezoelectric motor and the voltage developed across the electrical equivalent circuit. An integrating circuit receives the difference signal and provides a feedback signal to the controller. The difference signal is compared with the velocity signal to either increase or decrease the drive voltage applied to the piezoelectric motor so as to cause the piezoelectric motor to achieve the desired velocity.

What is claimed is: 
     
       1. A piezoelectric motor system, comprising: a piezoelectric motor incorporating an element that is physically displaced as a function of an applied voltage resulting in the generation of a back electromotive force;   controller means having an output connected to said piezoelectric motor, said controller receiving a direction signal indicating the desired drive direction of the piezoelectric motor and a velocity signal indicating the desired velocity of the piezoelectric motor, said controller providing a drive voltage for driving said piezoelectric motor in the desired drive direction;   an electrically equivalent circuit that mirrors the electrical characteristics of said piezoelectric motor connected to receive the drive voltage from said controller;   comparison means for providing a difference signal indicative of the difference in voltage developed across said piezoelectric motor and the voltage developed across said electrical equivalent circuit; and   integrating means for receiving the difference signal and for providing a feedback signal to said controller that is compared with the velocity signal to either increase or to decrease the drive voltage applied to said piezoelectric motor so as to cause the piezoelectric motor to achieve the desired velocity.   
     
     
       2. The piezoelectric motor system according to claim 1 and further comprising: a pair of buffer means, one for connecting the drive voltage from said controller means to said piezoelectric motor and the other for connecting the drive voltage to said electrically equivalent circuit means.   
     
     
       3. The piezoelectric motor system according to claim 1 and further comprising: a capacitor for coupling the difference signal to said integrating means for eliminating direct current components from entering the input to said integrating means. 
     
     
       4. A piezoelectric motor system comprising: a linear piezoelectric motor having a member that bends with the application of a voltage and generates a back electromotive force;   a mirror circuit that mirrors the electrical characteristics of the linear piezoelectric motor;   a controller for applying a drive voltage to said linear piezoelectric motor for driving the motor at a selected velocity; and   feedback means for detecting the voltage difference between the voltage developed across the linear piezoelectric motor and the mirror circuit which voltage difference is a function of the velocity of the linear piezoelectric motor, and for providing a driving signal to said controller for increasing or decreasing the drive voltage so as to cause the linear piezoelectric motor to drive at the selected velocity.   
     
     
       5. The piezoelectric motor system according to claim 4 and further comprising: a pair of buffer means, one for connecting the drive voltage from said controller to said linear piezoelectric motor and the other for connecting the drive voltage to said mirror circuit.   
     
     
       6. The piezoelectric motor system according to claim 4 and further comprising: an integrating means: and   a capacitor for coupling the difference signal to said integrating means for eliminating direct current components from entering the input to said integrating means.